FIG. 7 is a diagram illustrating the schematic structure of a conventional laser display.
This laser display 100 includes laser sources 101a˜101c corresponding to RGB primary colors and light modulators 106a˜106c for subjecting laser beams La˜Lc outputted from the laser sources 101a˜101c to intensity modulation according to primary color signals Sa˜Sc of an input video signal. The laser display 100 further includes a mirror 103 for reflecting the laser beam La modulated by the light modulator 106a, a dichroic mirror 102a for multiplexing the laser beam Lb modulated by the light modulator 106b and the laser beam La reflected at the mirror 103, and a dichroic mirror 102b for multiplexing the laser beam Lb modulated by the light modulator 106b and the laser beam outputted from the dichroic mirror 102a. Further, the laser display 100 includes a condenser lens 107 for condensing the laser beam that is obtained by the dichroic mirror 102b, a polygon scanner 104 for scanning the laser beam condensed by the condenser lens 107 in the x direction, and a galvanometer scanner 105 for scanning the light outputted from the polygon scanner 104 in the y direction so as to form a two-dimensional image on a screen 108.
Next, the operation will be described.
The laser beams La˜Lc emitted from the laser sources 101a˜101c corresponding to the RGB primary colors are subjected to intensity modulation by the light modulators 106a˜106c according to the respective primary color signals Sa˜Sc of the input video signal, respectively, and are multiplexed by the optical system comprising the mirror 103 and the dichroic mirrors 102a and 102b. Further, the laser beam condensed by the condenser lens 107 is scanned in the x direction by the polygon scanner 104 and in the y direction by the galvanometer scanner 105, whereby a two-dimensional image is displayed on the screen 108.
As described above, in the conventional laser display 100, since the light beams emitted from the RGB laser light sources 101a˜101c are monochromatic light beams, respectively, a bright image having a high color purity can be displayed by using the laser sources of appropriate wavelengths.
By the way, in the conventional laser display, since the laser sources which output high-coherent light beams are used as light sources, so-called speckle noise might occur. This speckle noise is a minute noise that occurs, when the laser beams are scattered on the screen 108, due to interference of the light beams which are scattered at the respective positions on the screen 108.
A method for removing such speckle noise is described in, for example, Japanese Published Patent Application No. Hei.7-297111. This literature describes a method of removing the above-mentioned speckle noise by rotating a diffuser which is disposed on an optical path of a condenser optical system.
However, a mechanism for rotating the diffuser causes an increase in the device scale. Further, loss of the light scattered by the diffuser causes a reduction in the brightness of the image displayed on the screen.
The present invention is made to solve the above-described problems and has for its object to provide a two-dimensional image formation apparatus which can prevent, using a diffuser, deterioration of an image due to speckle noise without increasing the device scale very much, and can perform bright image display by effectively reducing the loss of light that is scattered by the diffuser.